A continuing desire to tailor various vehicle functions and operations specifically to the size of a seat occupant has created a need for a non intrusive seat cushion pressure sensor to sense the actual weight of the seat occupant. From the sensed weight, the vehicle control system can, through suitable algorithms, extrapolate a height and size of the occupant based on standard human profiles. From the sensed weight and calculated height, occupant specific adjustments in other systems can be made.
One proposed pressure sensor is an air bladder, which is relatively simple and low cost. The bladder is comprised of a pressurized upper membrane with a sealed sensing volume below, which is forced down by the weight of the occupant. The consequent increase in air pressure in the bladder, read and measured by the vehicle's control system, would be used to calculate occupant weight. To work well, the bladder would have to be maintained within a given operative pressure range. Since the membrane material is inherently subject to a slow air pressure leakage, a means must be provided to make up for the leakage and maintain the proper bladder operating pressure. The current means to do so is an air pump and associated air accumulator, which senses whenever the bladder pressure has fallen below a defined threshold, and replenishes the bladder accordingly. Given the leakage rate of bladder, such a pump may need to cycle on and off quite frequently, and its size and capacity can be relatively large. The space within a vehicle interior available to store a pump and associated accumulator is limited, and the noise of frequent cycling may be objectionable.